Answer
See graph.
domain $(-\infty,\infty)$, range $[-3,3]$
Work Step by Step
Step 1. To graph $y=-3cos(2x)$, start from one period of $cos(x)$, shrink horizontally by a factor of $1/2$, stretch vertically by a factor of 3, then reflect across the x-axis. Repeat the resulting curve horizontally to cover more regions. See graph.
Step 2. We can determine the domain $(-\infty,\infty)$, range $[-3,3]$
